Welcome messages or MOTD for rooms

[matrixbot]

Created by @ matthew:matrix.org.

we should have the ability to show a para of text to users the first time they intersct with a room to include MOTD and COC info etc. the room would also see it as a message when updated

[ara4n]

This would be an m.room.purpose or m.room.motd event, i guess. It could also be achieved with a pinned message, but it'd be nicer if it only showed it on initial join.

[ara4n]

it'd be particularly nice to provide an intro paragraph for bot PM rooms.

[daniellekirkwood]

this has been tagged in the original "pinned messages" epic but we discussed internally that pinned messages does not solve this problem. we also have room topics, but they need iterating on. I will move this to a Discussion